This disclosure generally relates to rail components, and more particularly to rail components comprising flame retardant compositions containing specific combinations of siloxane block copolymers.
Flame retardant (FR) polymers and polymer blends, for example polycarbonates and polycarbonate blends with UL V0 and 5V A and B Underwriters Laboratories flammability ratings are widely prepared and used, especially in a wide variety of electrical and electronic applications. Conversely, only a very limited set of polycarbonates are used in certain railway applications, particularly interior parts for passenger rail cars such as windows, partition walls, ceiling panels, cabinet walls, storage compartments, galley surfaces, light panels, and the like. All of these applications have stringent flammability safety requirements that the polycarbonates must meet. Particular requirements include smoke density, flame spread, and heat release values. Furthermore, it is anticipated that rail requirements will approach or align with current aircraft standards. In the United States, Federal Aviation Regulation (FAR) Part 25.853 sets forth the airworthiness standards for aircraft compartment interiors. The safety standards for transportation systems used in the United States include a smoke density test specified in FAR 25.5 Appendix F, Part V Amdt 25-116. Flammability requirements include the “60 second test” specified in FAR 25.853(a) Appendix F, Part I, (a),1,(i) and the heat release rate standard (referred to as the OSU 65/65 standard) described in FAR F25.4 (FAR Section 25, Appendix F, Part IV), or the French flame retardant tests such as, NF-P-92-504 (flame spread) or NF-P-92-505 (drip test). In another example, the aircraft manufacturer Airbus has smoke density and other safety requirements set forth in ABD0031. In the event of a fire, components made from materials having these properties can increase the amount of time available for escape and provide for better visibility during a fire
Despite extensive investigation, current materials that meet these FAR standards (and thus potential rail standards) could be further improved with respect to other properties. Thus, there is a perceived need for polysulfones having improved melt flow, improved ultraviolet (UV) stability, and improved light transmission. Siloxane-polyestercarbonates have low melt flow and good color stability to indoor light, but may shift in color upon exposure to UV light. Certain polycarbonate-polyetherimide blends also have low melt flow, but can be difficult to formulate so as to provide bright white compositions.
In view of the current interior material safety standards, and in anticipation of more stringent standards in the future, materials that exceed governmental and aircraft or train manufacturer flame safety requirements are sought for current and anticipated rail applications. Such materials should also advantageously maintain excellent physical properties, such as toughness (high impact strength and high ductility). It would be a further advantage if such materials could be manufactured to be colorless and transparent. Still other advantageous features include good processability for forming articles, smooth surface finish, and light stability.